I think it is safe to assume that there will be equal to or less characters than in Brawl, because a giant roster would make it difficult to make each character individualized, and degrade the quality of the game.
Krom is pretty similar to Ike in regards to fighting style, so he's likely going to replace Ike. Ike's popularity matters little, because the current trend is two characters for Fire Emblem. Having three characters would only force a more deserving character from another franchise to get kicked off the list.
Matthew from Golden Sun may stand a chance, since he is from a Nintendo series. Since Namco Bandai is working with Nintendo this time, perhaps Lloyd Irving, or maybe a more recent tales protagonist.
I'd like to see Megaman in SSB, but as a third party character, anything could happen.
From the Metroid series, Anthony Higgs would be pretty cool to see in brawl, but Other M wasn't incredibly popular in comparison to other Metroid games. If anything Ridley could be added, but then there is the issue of size. Kraid should be playable.